Method and device for igniting and operating burners when gasifying  carbon-containing fuels

ABSTRACT

With a method and a device for igniting and operating burners when gasifying a carbon-containing fuel using at least two gasification burners, start of the pressure gasification with short start times is made possible, at high pressures, without prior inertization of the gas space, while avoiding continuous fuel gas consumption in the pilot burner or ignition burner and also protecting stationary ignition burners against contamination by configuring one gasification burner as a start-up burner, which is ignited by at least one pilot burner using an electrical ignition device. A combustible gas mixture including a fuel gas and oxygen-containing gas is ignited by the pilot burner, in the start-up burner. After ignition of the start-up burner, at least one further gasification burner is ignited by this burner. The start-up burner is operated further as one of the gasification burners of the carbon-containing fuel via a change in medium.

The invention is directed at a method for ignition and for operation of burners in the gasification of fuels that contain carbon, using at least two gasification burners.

Such a method of procedure, in which multiple dust burners are ignited by a pilot burner, is shown by DE 10 2005 048 488 A1. Other methods of procedure for ignition use so-called ignition lances, for example, as is shown by DE 32 27 155 A1, whereby passing such movable ignition aids through the firebox walls brings additional effort with it, and this leads to making such devices more expensive. Other examples are shown by EP 0 347 002 B1, EP 0 511 479 A1, U.S. Pat. No. 408,628, U.S. Pat. No. 5,273,212, DD 231 962 A, or DD 241 457 A.

With regard to the state of the art, reference is furthermore made to DE 196 41 843 A1, DE 195 29 994 C2, DE 100 24003 A1, DE 100 19 198 A1, DE 734 927 A, EP 0 095 103 B1, WO 2008/055829 A1, or AT 286 072 B.

A disadvantage of the known methods of procedure consists, among other things, in that the pilot burners or ignition burners continue to be kept in operation, and in this connection require a permanent through-flow of gas and oxygen or air, in order to prevent them from becoming plugged up by slag or the like. In this connection, it is particularly problematic to keep corresponding exit openings on the gasifier wall open at high slag flow. As has just been mentioned, the use of movable ignition lances is cost-intensive and problematic for other reasons. In this connection, access channels for gasification must be checked before introduction of the ignition burner, and usually cleaned, seals must be replaced, and more of the like, whereby this work must be carried out in the pressure-free state.

If this work must be carried out, the gasifier and the subsequent gas treatment, including H₂S and COS removal, must first be relaxed and made inert, whereby the fuel gases diluted with inert gas are usually burned off by way of a flare. After ignition of the ignition burner, the pressure then has to be raised slowly, for example 0.5 bar/min, and the inert gas must be displaced by the gas produced in the gasifier, whereby once again, the displaced gas, which is mixed with fuel gas, must be burned off in the flare. This method of procedure is not only time-consuming, but rather also has a high ignition fuel consumption with correspondingly high emission values caused by the flare.

This is where the invention takes its start, whose task consists in allowing start of the pressure gasification with short start times at high pressures, without prior inertization of the gas space, while avoiding continuous fuel gas consumption in the pilot burner or ignition burner, whereby in the case of stationary ignition burners, these are also protected against contamination.

This task is accomplished, according to the invention, with a method of procedure of the type indicated initially, in that one of the gasification burners is configured as a start-up burner, for the ignition of which at least one pilot burner serves, which is ignited by way of an electrical ignition device, whereby a combustible gas mixture composed of a fuel gas and gas that contains oxygen is ignited by the pilot burner, in the start-up burner, whereby after ignition of the start-up burner, at least one further gasification burner is ignited by this burner, and the start-up burner is operated further as one of the gasification burners of the fuel that contains carbon, by means of a change in medium.

By means of this ignition, which takes place in the manner of a cascade, a number of advantages are achieved, which particularly make it possible for ignition at high pressure to be possible, and to eliminate a movable or displaceable ignition device. In this way, the need to clean the access channel of the displaceable ignition burner before every start and to renew the seal of the corresponding channel is also eliminated. This method of procedure, according to the invention, particularly makes it possible for a plurality of gasification burners to be operated as start-up burners, with the use of a pilot burner during start-up.

A fast pressure increase before ignition of the gasification burner is possible without inertization of the gas space, and emissions during flare burn-off during shut-down and start-up are eliminated, to name only a few advantages.

Embodiments of the invention are evident from the dependent claims.

In this connection, individual pilot burners can be ignited, thereby making it possible to use the combustible mixture produced by the corresponding gasification burners and the flame formed from it to subsequently ignite the gas/oxygen mixture from other gasification burners. In this connection, the power and stability of the ignition flames are increased. These can then ignite further carbon burners, whereby the regulation and monitoring concept of the start routine is greatly simplified.

A further embodiment of the method of procedure according to the invention consists in that the pilot burner, after ignition of the start-up burner, additionally has a gas mixture applied to it that contains CO₂ and/or steam and/or oxygen, if applicable also inert gas, in order to prevent it from clogging, so that the pilot burner is fully integrated into the gasification system.

It is also advantageous if the pilot burner is first ignited at less than 50% of the power of the gasification burner that is operated as a gas burner, and at an oxygen excess number of 0.8 to 1.2, whereby it can also be provided that to accelerate the ignition of the mixture that contains oxygen, in the gasifier, the pilot burner has a fuel excess/oxygen excess number<0.8 applied to it.

An aid in ignition of the gasifier consists in monitoring the ignition flame of the pilot burner, whereby the flame is monitored in such a manner that the ignition element of the pilot burner is shut off when the flame is recognized.

If the flame is monitored using an ionization flame monitor, the ignition element of the pilot burner can be used as a corresponding electrode, as the invention also provides.

According to the invention, an optical flame monitor can be used, or the change in the electrical resistance of the ignition element can be used to recognize the flame.

The task formulated above is accomplished with a device, in that the pilot burner is equipped with a centric nozzle head, which is surrounded by a burner pipe, which projects beyond the nozzle head in the flow direction of the fuel gas, whereby at least one electrical ignition device is provided within the burner pipe space, and a reduction in cross-section of the burner pipe is provided in the flow direction behind it.

With this embodiment, it is possible to use an electrically heated ceramic glow element, for example. The reduction in cross-section in the burner pipe ensures a production of spin in the nozzle region, so that hot gas is passed back into the surroundings of the nozzle orifice, and the colder mixture of freshly supplied gases is ignited, and, in addition, a higher turbulence level can be set in order to bring about simple ignition. In this way, the flame can be stabilized by means of the corresponding constrictions.

As was already mentioned further above, it is important to monitor the flame of the pilot burner, whereby according to the invention, at least one flame monitoring element is assigned to the burner pipe, for example an optical flame monitoring device with a fiberglass line to a corresponding electronic component.

As will be described further below, the burner according to the invention has ring-shaped channels, whereby gas that contains oxygen is fed in through the first ring-shaped channel of the start-up burner, both during the ignition process and during normal operation, in such a manner that the orifice of the pilot burner is surrounded by a clean gas. If the pilot burner has a gas mixture applied to it after ignition, in order to prevent it from becoming clogged, this has the advantage that the fuel excess can react with the oxygen from the first ring channel.

Further characteristics, details, and advantages of the invention are evident from the following description and using the drawing. This shows, in

FIG. 1 a section through a pilot burner according to the invention, in a simplified representation,

FIG. 2 a top view of the pilot burner according to the arrow II in FIG. 1, and in

FIG. 3 a gasification burner with a centrally integrated pilot burner.

The device for ignition and for operation of burners in the gasification of fuels that contain carbon, designated in general with 1, is essentially formed by a pilot burner, represented schematically and in simplified manner in FIG. 1, and designated with 2, which burner has a fuel gas nozzle 3 to which the corresponding fuel gas is supplied at 4, whereby the fuel gas nozzle 3 is equipped with an air feed 5 that surrounds the fuel gas nozzle 3 concentrically. In the flow direction of an ignition flame, not shown in the figures, the nozzle head designated with 6 is surrounded by a burner pipe 7.

As can be seen in FIG. 1, an electrical ignition element, for example a glow element 9, which is connected with a corresponding power source by way of an electrical line 10, for igniting the fuel gas/air mixture, projects into the pipe space 8 formed by the burner pipe 7. In order to produce stable flames and optimal burner behavior, a constriction, indicated in general with 11, projects into the space formed by the burner pipe 7, in the orientation of the flame that is formed, in order to thereby bring about swirling or circulation of the gas, as indicated with an oval circle 12 in FIG. 1, with a broken line.

The pilot burner 2 is preferably situated in the central channel of the gasification burner, and is thereby protected from dirt by means of the gas that flows out through the inner ring channel. In addition, the central pilot burner channel can be flushed by means of a gas.

In addition, as is evident from FIG. 2, an optical flame monitoring element 13 can also be provided on the burner head 6, which element is surrounded by a protective pipe 14. In this connection, the sudden constriction 11 is not shown separately in FIG. 2, so that the elements 5 and 13 can be shown.

From FIG. 3, it is evident that the pilot burner 2 can represent an integral component of a gasification burner, indicated in general with 15, whereby the individual ring spaces and feed spaces of the gasification burner are reproduced in simplified manner here. This gasification burner 15 can be operated as a start-up burner, as has been described above.

In FIG. 3, the ring space or ring channel for primary oxygen is indicated with 16; 17 indicates the ring channel for the fuel, for example a gas or a dust suspension, 18 designates the ring channel for the secondary oxygen, and 19 designates the ring channel for inert or low-oxygen gas, for example N₂, CO₂, steam, or steam+O₂. Finally, in FIG. 3, 20 also designates the outer pipe of the gasification burner, 21 designates the orifice of the gasification burner, and 22 designates the orifice of the pilot burner.

Example for an advantageous media change in the pilot burner and the adjacent channels of the gasification burner.

Ignition Channel process Normal operation 4 Fuel gas No gas or a gasification medium or an inter gas 5 Gas that No gas, if the burner is directed contains downward, for example oxygen advantageously, a gasification medium that contains either O₂ and/or CO₂ or steam or a fuel gas that was supposed to be broken down in the gasifier 16 Gas that Gas that contains oxygen contains oxygen 17 Fuel gas Pneumatically conveyed fuel 18 Gas that Gas that contains oxygen contains oxygen There is also the possibility of having inert gas flow through the ring channels 16 to 19 to flush the channel, in each instance. In this way, for example, inert gas can flow through the channel 6, and thus prevent contamination in the region of the orifice of the pilot burner 22.

The size of the back-flow region 12 oval/circle can be influenced by means of the L/D ratio.

A monitoring element 13 for flame monitoring can be a lens system that has flushing air applied to it to prevent contamination, or also for cooling. This system can be surrounded with a protective pipe (FIG. 2, 14 protective pipe). A monitoring element can also be implemented by means of a suitable light guide system.

The monitoring element can be integrated parallel to the nozzle channel of the fuel gas line.

Another implementation possibility exists in such a manner that this monitoring element is integrated centrally within the fuel gas feed channel, so that flame monitoring takes place through the nozzle channel.

The monitoring element can recognize the flame of the pilot burner, for one thing, and, in the event that the pilot burner is shut off, can also be used to recognize a flame of the carbon burner, operated as a gas burner, by means of using the signal.

In this connection, the method of effect of the device according to the invention is the following:

Fuel gas and the air required for combustion are supplied to the pilot burner 2 or the central nozzle 3. This gas mixture flows into the interior of the burner pipe 7, designated as 8, into which the electrical ignition element, for example a glow element, designated as 9, projects, whereby the position of such a glow element is determined in such a manner that optimal ignition of the fuel/air mixture is guaranteed. This can be a location through which there is weak flow, for example, at which back-flow of the fuel gas/oxygen mixture takes place before ignition, or of the hot waste gas after ignition.

Not shown is the possibility that multiple glow elements 9 can be provided, which, as already mentioned above, can also be used to measure the ionization stream.

The burner pipe 7 can stabilize the flame within the pipe with a sudden constriction 11, whereby part of the hot waste gases are deflected by means of the constriction, and the circulation 12 is reinforced. As a result, the fresh, cold mixture of the supplied gases is reliably heated above the ignition temperature with the circulating hot waste gases. The flame penetrates from the burner pipe 7 into the gasification space, and there then ignites a combustible gas mixture of fuel gas and oxidation media, which flow out of the ring channels 16 to 19 of the gasification burner during the ignition phase. After the gasification burners have been ignited, gasification media such as CO₂, steam, or mixtures with oxygen can be passed to the combustion space not only by way of the fuel gas feed line of the pilot burner 4, but also by way of the air feed line 5, thereby ensuring that no dust deposits or caking form in the pilot burner.

Of course, the invention is not restricted to the exemplary embodiments that are shown. Further embodiments are possible without departing from the basic idea. For example, alternative injection of the corresponding media into the pilot burner can be modified and adapted to the cases of use, in each instance, the pilot burner can be operated at a fuel gas excess, the combustion media in the pilot burner can be formed by air or oxygen with nitrogen or CO₂ or with steam, in order to avoid soot formation at sub-stoichiometric combustion, for example, but the air can also be enriched with oxygen, the oxygen feed can be supplied with and without spin, and the like. 

1. Method for ignition and for operation of burners in the gasification of a fuel that contains carbon, using at least two gasification burners, wherein one of the gasification burners is configured as a start-up burner, for the ignition of which at least one pilot burner serves, which is ignited by way of an electrical ignition device, whereby a combustible gas mixture composed of a fuel gas and gas that contains oxygen is ignited by the pilot burner, in the start-up burner, whereby after ignition of the start-up burner, at least one further gasification burner is ignited by this burner, and the start-up burner is operated further as one of the gasification burners of the fuel that contains carbon, by means of a change in medium.
 2. Method according to claim 1, wherein after ignition of the start-up burner, the pilot burner has a gas mixture applied to it that contains CO₂ and/or steam and/or oxygen and participates in the gasification reactions, to prevent clogging.
 3. Method according to claim 1, wherein the pilot burner is first ignited at less than 50% of the power of the gasification burner being operated as a gas burner, and at an oxygen excess number of 0.8 to 1.2.
 4. Method according to claim 1, wherein in order to accelerate ignition of the mixture that contains oxygen in the gasifier, the pilot burner has a fuel excess/oxygen excess number<0.8 applied to it.
 5. Method according to claim 1, wherein the flame of the pilot burner is monitored and the ignition element of the pilot burner is shut off when the flame is recognized.
 6. Method according to claim 1, wherein an ionization flame monitor is used to monitor the flame of the pilot burner, whereby the ignition element is used as an electrode.
 7. Method according to claim 5, wherein an optical flame monitor is used, whereby the optical signal is passed to a detector by way of a lens and a light guide.
 8. Method according to claim 5, wherein the change in the electrical resistance of the ignition element is used to monitor the flame of the pilot burner.
 9. Device (1) for carrying out the method according to claim 1, wherein the pilot burner (2) is equipped with a centric nozzle head (3), which is surrounded by a burner pipe (7), which projects beyond the nozzle head (3) in the flow direction of the fuel gas, whereby at least one electrical ignition device (9) is provided within the burner pipe space (8), and a reduction in cross-section (11) of the burner pipe is provided behind that, in the flow direction.
 10. Device according to claim 9, wherein at least one flame monitoring element (13) is assigned to the burner pipe (7).
 11. Device according to claim 9, wherein the central nozzle head (6) is surrounded by a ring space that brings about the air or oxygen feed (5), in known manner, to feed in the fuel gas.
 12. Device according to claim 9, wherein the pilot burner (2) is positioned in the center of a gasification burner (15). 